The invention relates to a process for treating acid solutions, contaminated with uranium.
From a more general point of view, the invention is intended to provide a process for treating acid uraniferous solutions, possibly containing radium, which process comprises adjustment of the final pH and decontamination of uranium and of radium to values such that the solutions, after treatment, can be discharged without harming the natural environment.
The extraction of uranium ores from open pit mines or from underground mines necessitates treating the drained waters whose flow rates can reach several hundreds of cubic metres. These drained waters contain various elements, particularly uranium and possibly radium, at concentrations which can be detrimental to the natural environment when they are discharged thereto. In addition, these waters generally have a pH which is also detrimental to the natural environment.
It is the same with liquid effluents resulting from the acid or alkaline treatment of uranium ores.
In order not to spoil the natural environment particularly the hydrogeological system into which the drained waters and the liquid effluents are discharged the concentration of these waters and effluents respectively in uranium and radium must be as low as possible. This explains the reason why very strict standards have been fixed relating to the pH and the maximum content of uranium and of radium for drained waters and liquid effluents. It is necessary, in fact, for the final pH of the solutions to be between 5.5 and 8.5, for the radium content to correspond to an activity equal or less than 10 pCi/l and for the uranium content to be equal to or less than 1.8 mg/l.
It is known to remove the radium by a treatment with barium chloride, which in the presence of sulfate ions, causes the formation of barium sulfate and of radium sulfate which precipitate.
As for the removal of the uranium, in the processes employed until now, resins or other adsorbants (for example titanium oxide) are used, which require large installations and often are subject to risk of clogging.
The problem not yet resolved until now is the process of treating drained water or effluents, containing uranium content both too low to justify setting up of a laborious resin unit, and too high to permit discharge to to the natural environment.
The difficulties associated with the removal of the uranium are correlated to several parameters and particularly to the fact that, in uraniferous solutions, the uranium occurs in various physical forms, namely solid, soluble and colloidal.
The solid particles of uranium are generally the subject of removal by decantation or filtration.
As regards the soluble particles, their existence is explained by the use of sulfuric acid to form acid waters for the lixiviation of the uranium or by the presence of carbonate or bicarbonate ions used to form alkaline waters enabling the lixiviation of the uranium.
As for the colloidal particles, they correspond to an intermediate state between the solid and soluble uranium and they generally have a size of 10.sup.-1 to 10.sup.-3 microns and cannot be removed by simple decantation or filtration.
It is particularly the coexistence in the same solution of soluble and colloidal uranium which makes it difficult to set up a efficient process for removal of the uranium.
Another parameter which plays a part in the elimination of uranium, is the presence of numerous other ions as well as the respective values of their concentration. Among these ions, maybe be mentioned calcium, sodium; magnesium, sulfate, carbonate, bicarbonate, chloride, potassium, nitrate, ferric, or aluminum ions.
It is one of the objects of the invention to provide a process for removing uranium from acid uraniferous solutions, whether the uranium is soluable and/or in colloidal form.
It is another object of the invention to provide a process for removing uranium from acid uraniferous solutions, applicable even to solutions highly charged with ions.
Another object of the invention is to provide a process for removing uranium from acid uraniferous solutions, whatever the nature of the ion species in solution.
Another object of the invention is to provide a process for removing uranium and radium, from acid uraniferous solutions, at the end of which the contents of uranium and of radium and the value of the pH of the final solutions obtained are compatible with the natural environment.
A further object of the invention is to provide a process for removing uranium and radium from acid uraniferous solutions, at the end of which the contents of uranium and radium as well as the value of the pH of the final solutions obtained, meet the legislative standards in force.